Ornithopters A duck is a particular type of flying machine called an ornithopter. Typically the forces acting on flying object are modeled like this: This model is still valid with ducks, but the forces involved are not the same. In an airplane, lift and thrust are two separate forces, one provided by the wings and the other provided by the engine. Ducks do not have engines, and instead the thrust and lift are separate components of a single force vector produced by the wings. Ducks accomplish net thrust upwards by folding their wings when they flap up. This means that the tips of their wings do not follow an up and down motion, but rather in a circular motion. If ducks held their wings flat throughout each stroke, the force produced by moving their wings down would be the same as the force produced when moving them back up, resulting in no net force. By folding and drawing them inwards during the up stroke, they decrease their aerodynamic drag, which produces less force downwards